The Cell

• is the smallest structural and functional unit of life• functions are dictated by their specific structures/organelles

• Continuity of life has a cellular basis• All cells have some common structures and functions• Human cells have three basic parts:

• Plasma membrane—flexible outer boundary• Cytoplasm—intracellular fluid containing organelles• Nucleus—control center

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Lab 2, BIO 105

Cytoplasm• Located between plasma membrane and nucleus• Site where most cellular activities accomplished• Cytoplasmic Organelles• Membranous

• Mitochondria• Peroxisomes• Lysosomes• Endoplasmic reticulum• Golgi apparatus

• Nonmembranous

• Cytoskeleton • Centrioles • Ribosomes

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Plasma Membrane

• Phospholipid bilayer and proteins in a constantly changing “fluid mosaic “• small amount of cholesterol and glycolipids

• Plays a dynamic role in cellular activity• Is selectively permeable

• Determines what can enter and exit cell

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Membrane Lipids• Phospholipids (lipid bilayer)

• heads: polar (carries an electric charge) and attracted to water (hydrophilic)

• heads form the inner and outer surface of PM• tails: nonpolar and hydrophobic so they form the interior

area of the PM• small amount of cholesterol to increase membrane

stability and fluidity• Glycolipids--role is to provide energy and as markers for

cellular recognition. Carbohydrates are found on the outer surface of cell membranes.

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Plasma Membrane Proteins

Integral proteins

• Firmly inserted into the membrane (most span the width of the PM)

• Many float in the lipid bilayer to form a changing “mosaic pattern”

• Functions: Transport proteins (form channels and carriers), enzymatic activities, or receptors

Peripheral proteins• Loosely attached to integral proteins • Include filaments on intracellular surface and glycoproteins

on extracellular surface• Functions: Enzymes, motor proteins, cell-to-cell links,

provide support on intracellular surface, and form part of the glycocalyx (carbohydrate rich area on PM surface)

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Functions of Membrane Proteins

1. Transport2. Binding site for chemicals (i.e. hormones)3. Enzymatic activity4. Intercellular joining5. Cell-cell recognition: glycolipids identify your cells as

“yours” so foreign cells can be recognized by a lack of a “self” ID tag

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Membrane Transport• Plasma membranes are selectively permeable• Some molecules easily pass through the membrane; others do

not

Types of Membrane Transport • Passive processes

• No cellular energy (ATP) required• Substance moves down its concentration gradient

• Active processes• Energy (ATP) required• Substances typically move against the concentration gradient

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Cell TransportPassive Processes•occur because of kinetic energy of molecules•Substances move down the concentration gradient —from an area of high concentration to an area of lower concentrationoSimple diffusion —

o movement of solute throughout a solution (solvent)

oFacilitated diffusion—o Carrier-mediated-- moves through PM through a

carrier protein o Channel-mediated -moves through PM via a water

channel• Osmosis—movement of the solvent (water)– Filtration• Usually across capillary walls

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Osmosis•Movement of solvent (water) across a selectively permeable membrane •Water diffuses through plasma membranes down the concentration gradient :

• Through the lipid bilayer• Through water channels called aquaporins (AQPs)

•Water concentration is determined by solute concentration because solute particles displace water molecules•Water moves by osmosis until hydrostatic pressure (back pressure of water on membrane) and osmotic pressure (tendency of water to move into cell by osmosis) equalize•osmosis occurs until equilibrium is reached

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Importance of Osmosis

• When osmosis occurs, water enters or leaves a cell• Change in cell volume disrupts cell function

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Active Transport•Energy to do work comes from splitting the bonds within the ATP molecule OR •from the energy formed in the ionic gradient pumps create and used by the splitting of the ATP bonds to move substances

–Think of water being pumped uphill by an energy source; as some of the water leaks back downhill, it can carry substances with it; it co-transports substances

•Examples:–Vesicular transport—endocytosis and exocytosis

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–Types of Endocytosis:

• Phagocytosis—cell engulfs a relatively large or solid material i.e. bacteria

• Pinocytosis—cell engulfs a small amount of extracellular fluid containing dissolved molecules–Allows cell to “taste” extracellular fluids

• Receptor-mediated endocytosis —plasma membrane proteins which only bind certain substances

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LAB: TO DO1. Describe the phospholipid bilayer and how it functions as a semipermeable membrane.2. Describe process of diffusion and perform diffusion and dialysis experiments.3. Describe process of osmosis and how it can affect the cell. Perform the osmosis experiment.4. Describe process of filtration (as it pertains to function of human cells and tissues). Perform filtration experiment.

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